1. Field of the Invention
This invention relates to a catalyst and a process using the same for the production of olefinic polymers. The term olefinic polymers as used herein denotes both homopolymers and copolymers of olefinic hydrocarbons.
2. Prior Art
As disclosed in Japanese Patent Laid-Open Publication No. 58-19309, it has been proposed to produce ethylene homopolymers or ethylene-.alpha.-olefin copolymers among various polyolefins with use of a catalyst composition comprising a zirconium compound, typically a metallocene compound and an aluminoxane compound. This prior art catalyst is liable to form such a homopolymer or copolymer which is of a narrow molecular weight distribution and a low molecular weight and such a copolymer which has a relatively narrow composition distribution. However, the quality of polyolefins demanded by the relevant industry is such that they have a satisfactorily high molecular weight and a relatively wide molecular weight distribution and, in the case of copolymers, a narrow composition distribution.
With consideration given solely to an increase in the molecular weight of polyolefins, this may be achieved to some extent by the use of a selected metallocene compound. Japanese Laid-Open Patent Publication No. 63-251405 discloses the use of a dicyclopentadienyl hafnium compound. However, this hafnium compound is rather difficult to synthesize and inferior in catalytic activity to a dicyclopentadienyl zirconium compound. The hafnium compound is further disadvantageous in that the resultant polymers have a relatively narrow molecular weight distribution and, in the case of copolymers, fail to provide a composition distribution as narrow as desired.